Published in Physical Review Letters, the study posits that dark matter formed when these particles, initially moving at relativistic speeds, lost energy and gained mass after pairing up. This model departs from conventional views by proposing that dark matter began as high-energy particles that cooled dramatically, taking on mass as they slowed.
"Dark matter started its life as near-massless relativistic particles, almost like light," said Robert Caldwell, professor of physics and astronomy at Dartmouth and the study's senior author. "That's totally antithetical to what dark matter is thought to be-it is cold lumps that give galaxies their mass. Our theory tries to explain how it went from being light to being lumps."
This process, the researchers argue, could have left a detectable imprint on the Cosmic Microwave Background (CMB), the radiation left over from the Big Bang. Unlike conventional theories that view dark matter as inherently massive, this approach envisions it forming through a rapid phase change as particles cooled.
According to Caldwell and his co-author, Dartmouth senior Guanming Liang, these early particles bonded due to the opposing directions of their spin, similar to the magnetic alignment of the north and south poles. As the universe cooled, this spin imbalance caused a sudden energy drop, leading to the formation of the cold, heavy particles thought to constitute dark matter today.
"The most unexpected part of our mathematical model was the energy plummet that bridges the high-density energy and the lumpy low energy," Liang said. "At that stage, it's like these pairs were getting ready to become dark matter."
The researchers draw parallels to superconductivity, where massless particles can form Cooper pairs that conduct electricity without resistance. This mechanism, they suggest, supports the plausibility of dark matter formation through a similar transition.
Liang added, "The mathematical model of our theory is really beautiful because it's rather simplistic-you don't need to build a lot of things into the system for it to work. It builds on concepts and timelines we know exist."
Caldwell and Liang believe that ongoing and future CMB studies, including those by the Simons Observatory and CMB Stage 4, could provide the data needed to test their hypothesis.
"It's exciting," Caldwell said. "We're presenting a new approach to thinking about and possibly identifying dark matter."
Research Report:Cold Dark Matter Based on an Analogy With Superconductivity
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